The present invention relates to an outdoor electronics cabinet or the like having a back-up battery power source, and more specifically, to an outdoor electronics cabinet having a ventilated battery compartment that includes a thermal stabilizing unit for maintaining the temperature of the batteries within a specified range.
Outdoor electrical equipment cabinets in the telecommunications industry have traditionally included rectifier units to convert commercially supplied AC power to DC power. Battery back-up systems are employed so that service is maintained in the event of AC power failure. The predominant battery architecture currently used in these cabinets is the sealed valve-regulated lead acid (VRLA) battery.
The temperature extremes experienced annually in certain climatic zones substantially reduce the life of VRLA batteries. For instance, in Florida, the hot temperatures reached in the summer can reduce battery life by a factor of 4 or more. Conversely, freezing temperatures can reduce battery performance. To operate for their maximum lifetime, battery manufacturers generally recommend that the battery temperature be maintained above freezing and below about 80xc2x0 F. Accordingly, heating and cooling mechanisms are sometimes included with the battery to limit the thermal transients experienced by the VRLA batteries, thus prolonging battery life.
A VRLA battery emits hydrogen gas as it ages. An atmosphere with a hydrogen gas concentration above 4% is explosively flammable. Consequently, any chamber or cabinet used to house VRLA batteries must also be ventilated to prevent hydrogen gas build-up. However, this ventilation requirement complicates the task of maintaining the batteries within a desirable temperature range (i.e., through heating and/or refrigeration), since it inherently reduces the efficiency of any system employing active re-circulation of the air within the cabinet. This task is further complicated by the temperature fluctuations that typically accompany ventilation.
Accordingly, there is a need in the art for an outdoor electrical equipment cabinet which has a battery compartment that allows adequate ventilation for hydrogen gas to escape, while also maintaining the temperature of the battery within a prescribed range. There is also a need in the art for such a cabinet which is equipped with a mechanism for reducing temperature fluctuations. These and other needs are met by the present invention, as hereinafter described.
In accordance with the present invention, an electrical equipment cabinet is provided that includes an enclosure adapted to contain electrical equipment. A battery compartment, which is located in the enclosure, is adapted to contain at least one battery electrically coupled to the electrical equipment. The battery compartment has first and second opposing side walls, a bottom surface, and a first pair of vents located in the first and second side walls through which external air flows to remove heat. In addition, a second pair of vents, which are also located in the first and second side walls, allow gas emitted by the battery to escape by diffusion. A thermal stabilizing unit is disposed in the battery compartment for regulating the temperature of the battery in contact therewith. The thermal stabilizing unit has a conduit therein for conducting the external air flow between the vents in the first pair of vents.
In accordance with one aspect of the invention, the thermal stabilizing unit includes a thermally conductive element having first and second opposing surfaces. The first surface is adapted for supporting the battery. A heat sink is thermally coupled to the second surface of the thermally conductive element.
In accordance with another aspect of the invention, the conduit extends through the heat sink.
In accordance with another aspect of the invention, at least one thermoelectric module is provided for pumping heat from the battery to the heat sink. The thermoelectric unit is disposed between the thermally conductive element and the heat sink. The thermoelectric module may be a Peltier thermoelectric device.
In accordance with yet another aspect of the invention, the heat sink includes a substantially planar base and a plurality of parallel fins located on the base. In this case the conduit includes a plurality of channels defined by adjacent ones of the fins. Moreover, the conduit may further include at least one duct connecting the plurality of channels to a vent in the first pair of vents.
In accordance with another aspect of the invention, at least one resistive heating element is provided which is in contact with the thermally conductive element. The resistive heating element may be a rubber heating pad affixed to the thermally conductive element.
In accordance with another aspect of the invention, an insulating layer is disposed between the resistive heating element and the bottom surface of the battery compartment.
In accordance with still another aspect of the invention, a controller is provided for maintaining the temperature of the battery between upper and lower temperature setpoints. The controller may include an adjustment mechanism for selecting the upper and lower temperature setpoints. At least one temperature sensor may be electrically coupled to the controller for determining the temperature of the battery.
In accordance with another aspect of the invention, the battery compartment is configured as a slidable cabinet.
In accordance with yet another aspect of the invention, at least one support element is provided between the second surface of the thermally conductive element and the bottom surface of the battery compartment for supporting the weight of the battery. The support element may be a steel tube spacer, for example.
In accordance with another aspect of the invention, an air blower is provided in the conduit, which forces external air through the channels in the heat sink.
In accordance with still another aspect of the invention, an electrical equipment cabinet is provided which comprises a battery compartment segregated into at least first and second interior regions by means of a thermal stabilizing unit adapted to regulate the temperature of a battery in contact with the stabilizing unit. First and second vents are disposed in the first region, said first and second vents being in open communication with each other. Third and fourth vents are disposed in the second region, said third and fourth vents being in open communication with each other.